The invention relates to a reduction gear for rotational and pivotal movements, especially for measuring and driving units, which reduction gear can be coupled to the unit to be measured or to the drive and which generates a geared-down measuring movement extending the measuring range or a greatly geared-down driving movement.
Reduction gears for rotational and pivotal movements are known in driving simulators, for example, wherein, usually, the rotational angle of a steering wheel is electronically evaluated in the form of a 3D-simulation on a screen for representing a driving condition.
Recently, devices for measuring rotational angles and for counting rounds (rotations) have also been required for steering angle sensors in motor vehicles. However, in this case, there exist special requirements regarding the installation dimensions, functional safety and accuracy of the measuring device.
From U.S. Pat. No. 4,952,874, there is known a position detecting system with switchable reading units. This system is used for machine tools comprising a tool holder which is rotatable by 360xc2x0.
U.S. Pat. No. 4,145,608 proposes a device for detecting reference positions in rotating machine parts. This device is used, for example, for setting the ignition of internal combustion engines.
U.S. Pat. No. 5,567,874 shows a device for detecting rotational angles, for instance in throttle valves. This device can be used for converting rotational angles into corresponding resistance values.
To the extent that the prior art components are used to produce a steering angle sensor of the aforementioned type, the sensor consists of a first sensor unit whose rotor is coupled to the rotational movement of the steering wheel and a second sensor unit which has a rotation (rounds) counting function. The rotor of the second sensor unit is coupled to the rotor of the first sensor unit at a gear reduction ratio of 4:1 by a planetary gear. The rotational axes of the two rotors are arranged concentrically relative to one another. The inner rotor is connected to the steering spindle in a rotational way and, when the steering wheel rotates, the inner rotor drives the outer rotor of the second sensor unit, which outer rotor is driven via the planetary gear.
The concentric arrangement between the steering spindle, the rotor of the first sensor unit and the rotor of the second sensor unit means that the prior art steering angle sensor, in the radial direction relative to the longitudinal axis, requires a relatively large installation space. Furthermore, the sensor unit codings of prior art steering angle sensors are provided in the form of magnetic markings of the Gray Codes type, and the detection devices are so-called Hall sensors which, for the purpose of scanning the magnetic coding, are arranged at the circumference of the code disc. As a result, there are required relatively expensive hardware components which take up a great deal of space.
It is therefore an object of the present invention to develop a drive for measuring rotational angles and counting rounds of shaft axes and wheel positions, which drive comprises a measuring accuracy of xe2x89xa60.5 arc degrees within a temperature range of 40 to +80xc2x0 and whose maximum diameter is  less than 2 times the steering tube diameter with a maximum housing depth of one half {fraction (1/2 )}the diameter of a steering tube.
The present invention relates to an inventive reduction gear for rotational and pivotable movements, especially for measuring and driving units, which reduction gear can be coupled to the unit to be measured or to a driveshaft and which generates a geared-down measuring movement extending the measuring range or a greatly geared-down driving movement is mounted in the form of a differential planetary gear on a frame plate jointly with a rotatably supported angle diaphragm which enables the rotational angle and/or the number of rounds (rotations) of the object to be measured to be optically indicated. The differential planetary gear includes an input gear which is provided in the form of a change gear and which engages the driving ring gear of the unit to be measured. Next to the input gear, an internally toothed, annular reference gear is fixedly attached to the frame and wherein, between a pinion positioned on the hub of the input gear and the internal toothing of the reference gear, there is arranged a planetary gear which engages both the internal toothing and an output gear whose number of teeth differs from that of the reference gear. The output gear drives a pivot lever which engages a claw of the angle diaphragm. In a preferred embodiment, the input gear, the reference gear, the output gear and the pinion are arranged concentrically relative to a common axis.
It is advantageous for the angle diaphragm to be held under spring-pretension and for a cover plate to be arranged parallel to the frame plate, in which cover plate there are supported the axis and the angle diaphragm. The input gear is preferably provided in the form of a coupling for a driving unit and the output gear comprises a central shaft output end designed as an output unit. The input and output units are preferably supported in the frame plate and cover plate, with the reduction gear being flanged to the drive, thus forming one unit therewith.
The inventive reduction gear for measuring and driving purposes can be integrated into a steering angle sensor for example for determining the absolute angular position of the steering wheel of a motor vehicle. For this purpose, a first sensor unit is coupled to a second sensor unit. The first sensor unit includes a first rotor carrying a first coding and coupled to the rotational movement of the steering wheel and a detection device, for instance a sensor, arranged at the stator end and provided for scanning the coding of the rotor within one angle segment of the entire range of rotation of the steering wheel. The second sensor unit includes a rotor coupled via a gear to the rotor of the first sensor unit, of a coding movable by the rotor and of a detection device arranged at the stator end and provided for scanning the coding within the entire range of rotation of the steering wheel.
By use of one or more adjoining converter elements, the detection device of the first sensor unit can be converted into a sensor array, with the sensor array being suitable for scanning the coding of the rotor of the first sensor unit and for scanning the coding of the second sensor unit. The rotor 30 of the first sensor unit preferably is provided in the form of a code disc and the sensor array 20 extending radially relative to the rotational axis of the code disc and including the converter elements is arranged towards the flat side of the code disc carrying the coding.
In a preferred embodiment the gear coupling the rotor of the second sensor unit to the rotor of the first sensor unit is a differential planetary gear which comprises an input gear provided in the form of a change gear and engaging the driving ring gear of the first sensor unit, and, next to the input gear, an internally toothed, annular reference gear fixedly arranged at the frame. Between a pinion positioned on the hub of the input gear and the inner toothing of the reference gear there is arranged a planetary gear which engages both the inner toothing and the rotor of the second sensor unit, designed as an output gear, has a number of teeth which has been changed as compared to that of the reference gear. The rotor, through a pivot lever, engages a claw of an arm which carries the coding of the second sensor unit and is pivotably supported between the rotor and the sensor array.